Adults have 24 vertebrae that run from the base of the skull to the tailbone. Not only does this series of vertebrae form the spine, but it also houses nerves that run down from the brain and branch out to the body.

Discs, meanwhile, form the supportive cushions between vertebrae.

Each disc consists of a soft, jelly-like core – called the nucleus pulposus – which is surrounded by the annulus fibrosus, a firm, protective hoop made up of layers, much like the rings of an onion.

Sometimes, the annulus weakens and cannot do its job of holding the nucleus inside. Under the pressure of the vertebrae that sandwich it, the nucleus pushes on the annulus, which may bulge outward. This is called a herniated, slipped or torn disc. In some cases, the annulus is so damaged that some of the nucleus leaks out of a side of the ring – like a squeezed jelly donut.

This can cause pain in the back itself, or if the bulging disc pinches or presses on a nerve in the spine, the pain may shoot to the area of the body that the serve serves.

Most painful herniated discs happen in the discs of the power back, called the lumbar region. Nerves that branch from the lumbar spine go to the legs, so pain in the legs – or sciatica – is a frequent complaint. Disc problems in the neck, cervical region, may cause arm pain.

Not all disc problems come from accidents or trauma though. Some of them just occur naturally over a lifetime.

As discs become more rigid and less elastic with age, their chemistry can change and the discs may gradually dry, shrinking the space between vertebrae and leading to arthritis, bone spurs and pinched nerves. This is called degenerative disc disease.